Maybe the reason the install iso is 4GB is because you are getting the Ultimate Edition which is, effectively, Home+Pro+Tablet+Media Center+whatever else Microsoft has decided to throw in there.

And why the BT obsession? Because I feel it would be a lot more userfriendly than the current setup. Have those servers seed and then use the power of the internet and those wanting to download Vista to allow it do be done so as painlessly as possible. Direct download links died after 784k, the download manager keeps dying. BT, I'm sure, would be better than this.